1. Field of Disclosure
The present disclosure relates generally to an improved method of and apparatus for equipping hand-supportable bar code symbol reading systems with electronic article surveillance (EAS) tag deactivation capabilities.
2. Brief Description of the State of Knowledge in the Art
The use of bar code symbols for product and article identification is well known in the art. Presently, various types of bar code symbol scanners have been developed for reading bar code symbols at retail points of sale (POS).
Also, over the years, electronic article surveillance (EAS) methods have been developed to prevent shoplifting in retail stores or pilferage of books from libraries. Special tags are fixed to merchandise or books. These tags are removed or deactivated by the clerks when the item is properly bought or checked out at a POS station. At the exits of the store, a detection system sounds an alarm or otherwise alerts the staff when it senses “active” tags. For high-value goods that are to be manipulated by the patrons, wired alarm clips may be used instead of tags.
Currently, several major types of electronic article surveillance (EAS) systems have been developed, namely: magnetic-based EAS systems, also known as magneto-harmonic; acousto-magnetic based EAS systems, also known as magnetostrictive; and radio-frequency based EAS systems.
Magnetic-Based EAS Systems
In magnetic-based EAS systems, the tags are made of a strip of amorphous metal (metglas) which has a very low magnetic saturation value. Except for permanent tags, this strip is also lined with a strip of ferromagnetic material with a moderate coercive field (magnetic “hardness”). Detection is achieved by sensing harmonics and sum or difference signals generated by the non-linear magnetic response of the material under a mixture of low-frequency (in the 10 Hz to 1000 Hz range) magnetic fields. When the ferromagnetic material is magnetized, it biases the amorphous metal strip into saturation, where it no longer produces harmonics. Deactivation of these tags is therefore done with magnetization. Activation requires demagnetization. This type of EAS system is suitable for items in libraries since the tags can be deactivated when items are borrowed and re-activated upon return. It is also suitable for low value goods in retail stores, due to the small size and very low cost of the tags.
Acousto-Magnetic Based EAS Systems
These EAS systems are similar to magnetic-based EAS systems, in that the tags are made of two strips of metal, namely: a strip of magnetostrictive, ferromagnetic amorphous metal, and a strip of a magnetically semi-hard metallic strip, which is used as a biasing magnet (to increase signal strength) and to allow deactivation. These strips are not bound together, but are free to oscillate mechanically. Amorphous metals are used in such systems due to their good magneto-elastic coupling, which implies that they can efficiently convert magnetic energy to mechanical vibrations. The detectors for such tags emit periodic tonal bursts at about 58 kHz, the same as the resonance frequency of the amorphous strips[3]. This causes the strip to vibrate longitudinally by magnetostriction, and to continue to oscillate after the burst is over. The vibration causes a change in magnetization in the amorphous strip, which induces an AC voltage in the receiver antenna. If this signal meets the required parameters (correct frequency, repetition etc.) the alarm is activated.
When the semi-hard magnet is magnetized, the tag is activated. The magnetized strip causes the amorphous strip to respond much more strongly to the detectors, because the DC magnetic field given off by the strip offsets the magnetic anisotropy within the amorphous metal. The tag can also be deactivated by demagnetizing the strip, making the response small enough so that it will not be detected by the detectors. These tags are thicker than magnetic tags and are thus seldom used for books. However they are relatively inexpensive and have better detection rates (fewer false positives and false negatives) than magnetic tags.
Radio-Frequency Based EAS Systems
The Series 304 RF EAS label is essentially an LC tank circuit that has a resonance peak anywhere from 1.75 MHz to 9.5 MHz. The most popular frequency is 8.2 MHz. Sensing is achieved by sweeping around the resonant frequency and detecting the dip. Deactivation for 8.2 MHz label tags is achieved by detuning the circuit by partially destroying the capacitor. This is done by submitting the tag to a strong electromagnetic field at the resonant frequency which will induce voltages exceeding the capacitor's breakdown voltage, which is artificially reduced by puncturing the tags.
The Unsolved Problem
Despite numerous advances in EAS systems over the past few decades, enabling conventional bar code symbol readers with EAS capabilities, at the time of manufacture, as well after purchase during upgrading efforts, has been both a component and labor intensive activity.
Therefore, there still remains a great need in the art for an improved method of and apparatus for enabling hand-supportable and countertop-supportable bar code symbol reading systems with electronic article surveillance (EAS) capabilities, while avoiding the shortcomings and drawbacks of prior art systems and methodologies.